diff --git a/packages/core/src/prompts/promptProvider.test.ts b/packages/core/src/prompts/promptProvider.test.ts
index e01e8bcba1..6fcfd685fd 100644
--- a/packages/core/src/prompts/promptProvider.test.ts
+++ b/packages/core/src/prompts/promptProvider.test.ts
@@ -358,7 +358,7 @@ describe('PromptProvider', () => {
       const provider = new PromptProvider();
       const prompt = provider.getCoreSystemPrompt(mockConfig);
 
-      expect(prompt).toContain('[Active Topic: Active Chapter]');
+      expect(prompt).toContain('<active_topic>\nActive Chapter\n</active_topic>');
     });
 
     it('should NOT include active topic context when narration is disabled', () => {
@@ -369,7 +369,7 @@ describe('PromptProvider', () => {
       const provider = new PromptProvider();
       const prompt = provider.getCoreSystemPrompt(mockConfig);
 
-      expect(prompt).not.toContain('[Active Topic: Active Chapter]');
+      expect(prompt).not.toContain('<active_topic>\nActive Chapter\n</active_topic>');
     });
 
     it('should filter out update_topic tool when narration is disabled', () => {
diff --git a/packages/core/src/prompts/promptProvider.ts b/packages/core/src/prompts/promptProvider.ts
index fac9085392..0d6a32980f 100644
--- a/packages/core/src/prompts/promptProvider.ts
+++ b/packages/core/src/prompts/promptProvider.ts
@@ -280,8 +280,8 @@ export class PromptProvider {
       if (activeTopic) {
         const sanitizedTopic = activeTopic
           .replace(/\n/g, ' ')
-          .replace(/\]/g, '');
-        sanitizedPrompt += `\n\n[Active Topic: ${sanitizedTopic}]`;
+          .replace(/[\[\]<>]/g, '');
+        sanitizedPrompt += `\n\n<active_topic>\n${sanitizedTopic}\n</active_topic>`;
       }
     }
 
diff --git a/packages/core/src/prompts/snippets.legacy.ts b/packages/core/src/prompts/snippets.legacy.ts
index f2c8bb2b33..1bec30db9f 100644
--- a/packages/core/src/prompts/snippets.legacy.ts
+++ b/packages/core/src/prompts/snippets.legacy.ts
@@ -527,6 +527,7 @@ function mandateTopicUpdateModel(): string {
 ## Topic Updates
 As you work, the user follows along by reading topic updates that you publish with ${UPDATE_TOPIC_TOOL_NAME}. Keep them informed by doing the following:
 
+- **No topic markers in chat:** Never include topic markers, title text, or the active topic marker (e.g. \`[active topic]\` or \`<active_topic>\`) in your chat responses. All topic and progress updates MUST be communicated exclusively via the ${UPDATE_TOPIC_TOOL_NAME} tool.
 - Usage Exception: NEVER use ${UPDATE_TOPIC_TOOL_NAME} for answering questions, providing explanations, or performing isolated lookup tasks (e.g. reading a single file, running a quick search, or checking a version). It is STRICTLY for orchestrating multi-step codebase modifications or complex investigations involving 3 or more tool calls.
 - Always call ${UPDATE_TOPIC_TOOL_NAME} in your first turn.
 - For tasks taking multiple turns, also call ${UPDATE_TOPIC_TOOL_NAME} in your last turn to recap what was done.
diff --git a/packages/core/src/prompts/snippets.ts b/packages/core/src/prompts/snippets.ts
index 385e8ffb22..e619a18a41 100644
--- a/packages/core/src/prompts/snippets.ts
+++ b/packages/core/src/prompts/snippets.ts
@@ -656,6 +656,7 @@ function mandateTopicUpdateModel(): string {
 ## Topic Updates
 As you work, the user follows along by reading topic updates that you publish with ${UPDATE_TOPIC_TOOL_NAME}. Keep them informed by doing the following:
 
+- **No topic markers in chat:** Never include topic markers, title text, or the active topic marker (e.g. \`[active topic]\` or \`<active_topic>\`) in your chat responses. All topic and progress updates MUST be communicated exclusively via the ${UPDATE_TOPIC_TOOL_NAME} tool.
 - Usage Exception: NEVER use ${UPDATE_TOPIC_TOOL_NAME} for answering questions, providing explanations, or performing isolated lookup tasks (e.g. reading a single file, running a quick search, or checking a version). It is STRICTLY for orchestrating multi-step codebase modifications or complex investigations involving 3 or more tool calls.
 - Always call ${UPDATE_TOPIC_TOOL_NAME} in your first turn.
 - For tasks taking multiple turns, also call ${UPDATE_TOPIC_TOOL_NAME} in your last turn to recap what was done.